Contactless wafer positioning carrier design

Abstract

A method of wafer handling includes providing a wafer on a wafer carrier on a wafer chuck on a vacuum plate. The wafer carrier includes a permanent magnet. The wafer chuck includes an electromagnet. The wafer is raised against a gravity direction by flowing an electrical current through the electromagnet so that the wafer carrier is repelled from the wafer chuck while the wafer remains on the wafer carrier. While keeping the wafer raised, wafer alignment is adjusted by moving the wafer chuck, the wafer carrier or both. The electrical current is reduced to zero so that the wafer carrier contacts the wafer chuck. The wafer is connected to the vacuum plate via a first vacuum cavity of the wafer chuck and a third vacuum cavity of the wafer carrier. The wafer carrier is connected to the vacuum plate via the second vacuum cavity of the wafer chuck.

What is claimed is: 
     
         1 . A method of wafer handling, the method comprising:
 providing a wafer, a wafer carrier, a wafer chuck and a vacuum plate, wherein the wafer is on the wafer carrier, the wafer carrier is on the wafer chuck, the wafer chuck is on the vacuum plate, the wafer carrier comprises a permanent magnet, the wafer chuck comprises an electromagnet, the wafer chuck comprises a first vacuum cavity and a second vacuum cavity, the wafer carrier comprises a third vacuum cavity;   while a vacuum for the first vacuum cavity, the second vacuum cavity and the third vacuum cavity is off, raising the wafer against a gravity direction by flowing an electrical current through the electromagnet so that the wafer carrier is repelled from the wafer chuck while the wafer remains on the wafer carrier;   while keeping the wafer raised, adjusting wafer alignment by moving the wafer chuck, the wafer carrier or both so that the first vacuum cavity and the third vacuum cavity are aligned with each other; and   reducing the electrical current to zero so that the wafer carrier is in contact with the wafer chuck, wherein the wafer is connected to the vacuum plate via the first vacuum cavity and the third vacuum cavity, and the wafer carrier is connected to the vacuum plate via the second vacuum cavity.   
     
     
         2 . The method of  claim 1 , wherein:
 the first vacuum cavity and the second vacuum cavity include through-holes that extend through the wafer chuck, and   the third vacuum cavity includes a through-hole that extends through the wafer carrier.   
     
     
         3 . The method of  claim 1 , wherein:
 an overall area of the first vacuum cavity and the second vacuum cavity in a horizontal plane substantially perpendicular to a thickness direction of the wafer chuck is larger than an overall area of the third vacuum cavity in the horizontal plane.   
     
     
         4 . The method of  claim 1 , wherein:
 the first vacuum cavity and the second vacuum cavity are not connected with each other.   
     
     
         5 . The method of  claim 1 , wherein:
 the first vacuum cavity and the second vacuum cavity are part of a stripe pattern and connected with each other.   
     
     
         6 . The method of  claim 1 , further comprising:
 switching on the vacuum for the first vacuum cavity, the second vacuum cavity and the third vacuum cavity so that the wafer, the wafer carrier, the wafer chuck and the vacuum plate are held together by the vacuum.   
     
     
         7 . The method of  claim 6 , further comprising:
 rotating the wafer by a robot gripper so that a working surface of the wafer is not perpendicular to the gravity direction.   
     
     
         8 . The method of  claim 7 , wherein:
 the wafer is rotated so that the working surface of the wafer is parallel to the gravity direction.   
     
     
         9 . The method of  claim 6 , further comprising:
 flowing another electrical current through the electromagnet so that the wafer carrier is magnetically attracted to the wafer chuck.   
     
     
         10 . The method of  claim 1 , wherein:
 the wafer carrier further comprises a dielectric enclosure, and the permanent magnet is embedded in the dielectric enclosure.   
     
     
         11 . The method of  claim 10 , wherein:
 the wafer carrier further comprises wafer pins outside the dielectric enclosure.   
     
     
         12 . An apparatus for wafer handling, the apparatus comprising:
 a wafer chuck comprising an electromagnet and configured to receive a wafer carrier thereon, the wafer carrier comprising a permanent magnet and configured to receive a wafer thereon, wherein the wafer chuck comprises a first vacuum cavity and a second vacuum cavity, and the wafer carrier comprises a third vacuum cavity;   a vacuum plate below the wafer chuck, wherein the wafer is configured to connect to the vacuum plate via the first vacuum cavity and the third vacuum cavity, and the wafer carrier is configured to connect to the vacuum plate via the second vacuum cavity; and   a controller that is configured to, while a vacuum for the first vacuum cavity, the second vacuum cavity and the third vacuum cavity is off, raise the wafer against a gravity direction by flowing an electrical current through the electromagnet so that the wafer carrier is repelled from the wafer chuck while the wafer remains on the wafer carrier.   
     
     
         13 . The apparatus of  claim 12 , wherein:
 the first vacuum cavity and the second vacuum cavity include through-holes that extend through the wafer chuck, and   the third vacuum cavity includes a through-hole that extends through the wafer carrier.   
     
     
         14 . The apparatus of  claim 12 , wherein:
 an overall area of the first vacuum cavity and the second vacuum cavity in a horizontal plane substantially perpendicular to a thickness direction of the wafer chuck is larger than an overall area of the third vacuum cavity in the horizontal plane.   
     
     
         15 . The apparatus of  claim 12 , wherein:
 the first vacuum cavity and the second vacuum cavity are not connected with each other.   
     
     
         16 . The apparatus of  claim 12 , wherein:
 the first vacuum cavity and the second vacuum cavity are part of a stripe pattern and connected with each other.   
     
     
         17 . The apparatus of  claim 12 , wherein:
 the wafer carrier further comprises a dielectric enclosure, and   the permanent magnet is embedded in the dielectric enclosure.   
     
     
         18 . The apparatus of  claim 17 , wherein:
 the wafer carrier further comprises wafer pins outside the dielectric enclosure.   
     
     
         19 . The apparatus of  claim 12 , further comprising:
 a robotic gripper that is configured to rotate the wafer so that a working surface of the wafer is not perpendicular to the gravity direction.   
     
     
         20 . The apparatus of  claim 12 , wherein:
 the controller is further configured to move the wafer chuck to adjust wafer alignment while keeping the wafer raised, before reducing the electrical current to lower the wafer along the gravity direction.